The correct answer is: d. the Bosporus, the Sea of Marmara, the Dardanelles
The Black Sea provides Russia with a warm-water outlet to the Aegean and Mediterranean Seas through the Bosporus, the Sea of Marmara, and the Dardanelles.
So, when it's mentioned that "the Black Sea provides Russia with a warm-water outlet to the Aegean and Mediterranean Seas by way of the Bosporus, the Sea of Marmara, and the Dardanelles," it means that ships leaving the Black Sea can navigate through these waterways to reach the Aegean Sea and the Mediterranean Sea. This is important for Russia because it provides access to warmer waters that are not frozen during winter, allowing for year-round navigation and trade.